The present invention relates generally to a fluid shear coupling apparatus, and more specifically to a coupling of this type having a modulating valve.
Fluid shear coupling devices have various applications, and are well-suited, for example, to drive a radiator cooling fan of an internal combustion engine. In order to avoid needless waste of engine energy, fluid shear couplings have been developed which modulate or vary the rotational speed of the cooling fan according to cooling requirements. As temperature increases, the fan speed increases to provide additional cooling. When engine temperature is lower, fan speed is kept lower, thus avoiding wasting energy by driving the fan at speeds higher than are necessary.
This speed modulation is accomplished by varying the level of viscous liquid in the shear coupling. By increasing the amount of liquid providing shear between the rotating input member and the rotating output member (having, for example, a fan thereon), the speed of the output member increases more nearly to the speed of the input member.
One approach to such fluid coupling modulation is disclosed in U.S. Pat. No. 4,502,580 in which a valve member moves with respect to the fluid reservoir cover, exposing a fluid flow opening of varying size with its outermost point moving radially outward and with its outermost edge being oriented at an acute angle relative to a radially extending line. The flow opening is not of a constant area, and the valve member rotates about the common axis of the rotating output member.
Another approach is disclosed in U.S. Pat. No. 4,627,524 which also has a valve member which moves with respect to the fluid reservoir cover. Various discreet openings are located in the reservoir cover, which vary the fluid flow area and the fluid level depending on the location of the valve member. As before, the flow opening is not of a constant area, and the valve member rotates about the common axis of the rotating output member.
Another approach is disclosed in my earlier U.S. Pat. No. 4,653,624. Other related devices are disclosed in U.S. Pat. Nos. 4,403,757, 4,446,952, 4,469,209, 3,463,282, 3,587,801, 3,943,893, 4,295,550, 4,298,111, 4,555,004, 4,086,987, 4,036,339, 3,642,105, and 4,437,554.
The present invention is a significant improvement over these other devices. The present invention provides greater flexibility in shear coupling design, and allows for the sensitivity of modulation to be varied. In addition to variable sensitivity, the present invention allows for greater responsiveness in fluid level for a given temperature change. Furthermore, the present invention allows for a constant fluid inlet flow area while still providing fluid level modulation.
These benefits are realized by a selected arrangment of the valve member with respect to the reservoir cover and by a selected arrangement of the openings in the valve member and the reservoir cover. More specifically, the present invention provides for the valve member to pivot on an axis of rotation which is eccentric to, and radially outward of, the common axis of rotation of the output member housing. Another aspect of the present invention is to have the fluid inlet flow aperture remain a constant size while still providing fluid level modulation and corresponding rotational speed modulation.